Dynamic memory cells store a charge on a capacitor. The capacitor loses its charge over time and must be periodically refreshed. This refresh operation consumes resources and locks up the memory from performing other operations during the refresh, such as reading and writing. The frequency with which a particular capacitor will need refreshing depends on the construction and manufacture of the chip. On the same chip and often the same row, some capacitors may hold a charge on the order of milliseconds, while other capacitors may hold a charge on the order of seconds.